The present invention relates to the field of wireless communication and data transfer devices. More particularly, the present invention relates to a new class of embedded antenna designs offering superior directional performance over at least two radio frequency bands and tolerance for diverse polarization angles for incoming signals regardless of the spatial orientation of the portable wireless communication device into which the antenna is embedded.
A variety of prior art antenna designs are currently used in wireless communication devices. One type of well known and used antenna design is an external half wave single or multi-band dipole type and another is the planar inverted-F antenna (PIFA) type.
The first type of antenna typically extends or is extensible from the body of a wireless communication device (WCD) in a linear fashion. While this type of antenna is acceptable for use in conjunction with some WCDs, several drawbacks impede greater acceptance and use of such external half wave single or multi-band dipole antennas. One significant drawback is that the antenna is typically mounted at least partially external to the body of a WCD which places the antenna in an exposed position where it may be accidentally or deliberately damaged, bent, broken, or contaminated. Furthermore, due to the physical configuration of this class of antenna, optimizing performance for a particular directional signal. That is, these types of prior art antennas are relatively insensitive to directional signal optimization or, said another way, these types of prior art antennas can operate in a variety of positions relative to a source signal without substantial signal degradation. This performance characteristic is often known as an xe2x80x9comni-directionalxe2x80x9d quality, or characteristic, of signal receipt and transmission. This means that electromagnetic waves radiate substantially equally in all directions during transmitting operations. Such prior art antennas also are substantially equally sensitive to receiving signals from any given direction (assuming adequate signal strength). Unfortunately, for a hand held WCD utilizing such a prior art antenna, the antenna radiates electromagnetic radiation equally toward a human user of the WCD equipped with such an antenna.
The second type of antenna known as a PIFA design, is operable in a single frequency band and consists of a rectangular metallic plate resonator element disposed above and parallel to a ground plane with a terminal electrically coupled to a ground plane of reduced electrical potential formed at one comer of the rectangular resonator plate and a communication signal feed terminal along an edge of the rectangular resonator plate closely space from the ground terminal. The rectangular resonator plate often has contiguous side panels bent in the direction of the ground plane. The PIFA is electrically connected to circuitry of the WCD to send and receive communication signals in the form of radio frequency (RF) electromagnetic radiation.
There is essentially no so-called xe2x80x9cfront-to-back ratioxe2x80x9d (with respect to a WCD) and little or no reduction in the specific absorption rate (SAR) with this type of prior art antenna design. For reference, a typical SAR value is usually expressed as follows: 2.7 mw/g at a 0.5 watt transmission power level. For further reference, for multi-band versions of prior art types of antenna, the external half wave single or multi-band dipole antenna (i.e., where resonances are achieved through the use of inductor-capacitor (LC) traps), signal gain on the order of approximately a positive two decibels (+2 dBi) are common and expected.
In addition, due mainly to the inherent shape of such prior art antennas, when operating they are typically primarily sensitive to receiving vertical polarization communication signals and may not adequately respond to communication signals that suffer from polarization rotation due to the effects of passive reflection of the communication signals between source and receiver equipment. Furthermore, such prior art antennas are inherently inadequate in sensitivity to horizontal polarization communication signals.
Another type of prior art antenna useful with portable wireless communication gear is an external quarter wave single or multi-band asymmetric wire dipole. This type of antenna operates much like the aforementioned external half-wavelength dipole antenna, but requires an additional quarter wave conductor to produce additional resonances and, significantly, suffers the same drawbacks as the aforementioned half wave single band, or multi-band, dipole antenna.
Therefore, the present invention recognizes and addresses herein a need in the art of antenna design for a WCD for an antenna assembly which is compact and lightweight; that is less prone to breakage and has no moving parts (which may fail, become bent, and/or misaligned), and, which utilizes the available interior spaces and structure of a WCD to achieve a more compact final configuration.
There is also a need for an antenna assembly which is able to receive and transmit electromagnetic frequencies at one or more preselected operational frequency bands.
There is also a need in the art for a deformable antenna resonator which is equally responsive to a variety of different communication signals having a variety of polarization orientations and emanating to and from diverse directions.
There also exists a need in the art for an antenna assembly which is compact and lightweight and which can receive and transmit electromagnetic signals at one or more discrete frequencies and which antenna assembly can be tuned to one or more frequencies.
The invention herein taught, fully enabled, described and illustrated in detail herein is a low-profile multiple band antenna assembly for use in a compact wireless communication device (WCD) which meets the shortcomings of the prior art. The inventive antenna assembly of the present invention includes a resonator element comprising a complex substantially hemispherical, or a curving, topography and having a complex set of linear peripheral edges. In addition, the ground terminal location and the signal feed terminal location are not located along an end region of the complex-shaped resonator element, and are preferably disposed closely spaced apart in a central region of the complex-shaped resonator element. In one embodiment of a new class of hybrid-PIFA type designs taught herein, the complex-shaped resonator element comprises a film or layer of electrically conducting material formed on a suitable shaped dielectric substrate. In another embodiment of the present invention, the complex resonator element comprises a metallic member formed into suitable complex shape by traditional metal stamping techniques. In yet another embodiment, the complex-shaped resonator element is formed of electrically conducting resin or polymer materials and may be molded, stamped, or thermally treated and pressed into a desired complex shape.
The resonator element may be shaped in a variety of other ways to create a surface topography having a desired three-dimensional contour as compared to traditional planar PIFA designs. The ground plane comprises an electrically conductive region of reduced electrical potential. The ground plane may disposed as a single layer of conductive material, or may comprise several electrically connected layers of conductive material, and typically is disposed on or within a printed wiring board, or other substrate member, used to support diverse electrical circuitry that affect WCD communication.
Herein, the term xe2x80x9cresonator elementxe2x80x9d shall refer generally to the overall complex surface topography of the complex-shaped conductive material and the term xe2x80x9cresonator segmentsxe2x80x9d shall refer to the discrete angular edge portions of said resonator element. Many variations of the resonator element and the resonator segments are possible and useful in practicing the present invention, including a wide variety of discrete resonator segments spaced from and disposed relative to the ground plane in a non-parallel orientation.
These resonator segments are preferably spaced at various elevations apart from a ground plane member of a wireless communication device (WCD) and together comprise the resonator element which is preferably curved, or hemispherical, in cross-section and may itself be disposed at a different elevation, or height, with respect to the ground plane member. The precise shape, location, and spacing of the resonator segments relative to the ground plane can be designed and fabricated to optimize response to discrete frequency bands and optimize antenna performance as embedded into diverse housing configurations and in anticipation of the typical manner is which a human operator operates, stores, holds and places a WCD (e.g., a WCD held upright, inverted, covered, uncovered, open, closed, etc.). In addition, the class of inventive antennas taught herein are designed to conform to an interior portion of a compact, low-profile WCD (i.e,. thin or narrow in elevational cross section).
In the present invention, the resonator segments are either disposed on and supported by a substrate or formed of an electrically conductive material, or materials, and arranged and electrically connected to a ground plane associated with the WCD. Whether or not disposed on a substrate, the resonator element is oriented to best capture RF communication signals.
The flexible dielectric support substrate is preferably comprised of a material having suitable dielectric and thermal cycling properties (e.g., non-electrically conducting laminated epoxy, lower temperature ABS material, cyanate ester, polyimides, PTFE, composites, amalgams, resin-based material, ceramic, etc. with due consideration for costs and benefits of each). Some specifications for a dielectric support usable in conjunction with preferred embodiments of the present invention include: a dielectric constant having a magnitude of approximately three (within a range dielectric constant of about 1 to about 20), low loss, and high temperature resilience (with respect to swelling, warping, and the like) during solder reflow during fabrication, and tolerance for thermal cycling generally. A particularly preferred dielectric substrate is produced and distributed by The Dow Chemical Company under the Questra(copyright) brand name. This product is a crystalline polymer featuring excellent heat resistance; high tolerance to chemicals and harsh environments; is very moldable; and moisture resistant. Typical applications for this product include automotive connectors, switches, and engine components; electrical connectors; phone jacks; circuit board connectors and the like. With respect to the xe2x80x9cdeformablexe2x80x9d characteristic of the resonator member, said characteristic is useful primarily during manufacture of the antenna assembly of the instant invention and does not contribute generally to the functionality of the resulting antenna assembly. At least during fabrication processing, in the case where the resonator element is disposed on a portion of a deformable dielectric substrate, the substrate should be sufficiently deformable so that after initially forming the complex shape of the substrate, the substrate retains its desired shape. After forming the appropriate shape for the resonator element the conductive resonator element is preferably coupled to the substrate. The resonator element may be formed by: deposition, adhering a conductive film, electo-less plating and/or electo-plating and other techniques as known and used in the art. The resulting antenna assembly clearly may occupy heretofore unusable interior space within a compact, low-profile WCD and permits fabrication of a variety of antenna shapes and configurations depending on such usable interior space within a particular WCD and desired frequency bands for communicating via the WCD. The class of antenna designed and fabricated according to the present invention and for which precise dimensions, illustrations, and performance data is presented herewith (see FIG. 2), operates with superior directional response over the 900 MHz cellular WCD frequency band (i.e., 880 MHz to 960 MHz) and the 1800 MHz personal communication system (PCS) frequency band (i.e,. 1850 MHz to 1990 MHz). The flexibility of preferred substrate material allows for variety in shape so that a wide variety of other frequency bands may be accommodated, including the 2.45 GHz frequency band and others.
An antenna assembly according to the present invention may be attached in many different locations with respect to the WCD, including discrete single or multiple locations disposed in the interior, the exterior, and/or located at discrete locations along the periphery of electronics disposed within a portion of the housing of the WCD, and the like. However, the preferred location is at an upper end of a WCD and more preferably, with a resonator element that is continuously curved, conforming closely to corresponding sloping upper end of a WCD. However, many other configurations are possible and clearly within the purview of those skilled in the art to which the present invention is directed. One such configuration is wherein the resonator element is formed integrally with the exterior housing of a WCD. For example, as one layer of a non-conductive portion of such a housing, such as a polymer or resin-based housing material. If a metallic housing is used generally for a given WCD design, the resonator element may be disposed in a location where opaque or transparent material is used so that no or just nominal RF signal loss occurs near the resonator element. While not preferred, if a metallic housing entirely envelopes a WCD, the resonator element may be attached or mechanically coupled to the exterior of said metallic housing and electrically coupled to the ground plane and the operative WCD signal processing circuitry on the interior. In this integrated WCD housing/antenna assembly the antenna is not technically xe2x80x9cembeddedxe2x80x9d inside the WCD, and thus suitable protective layering or applique may be applied to protect the resonator element and help promote stability to the particular topography of the resonator element and the discrete resonator segments thereof.
As will be appreciated by those of skill in the art to which the invention is directed, the size, shape, physical configuration, electrical and frequency performance characteristics of the antenna assembly will depend in part on the particulars of a given WCD design iteration in view of desired operating frequency (or frequencies), interior dimensions, electrical power constraints, composition of WCD components, and the like. Further, the antenna assembly may be coupled to a WCD at a variety of locations, including the interior, the exterior, within a portion of the housing of the WCD itself, and may be coupled via a suitable antenna interface outlet using conventional components.
It is an object of the present invention to provide a compact antenna assembly designed to be incorporated into a variety of WCDs by conforming to diverse locations in the interior space of such devices.
It is another object of the present invention to reduce the potential for damage and/or breakage of traditional antenna design by reducing external parts to a minimum and firmly mounting antenna assembly components to pre-existing structure of compact WCDs.
It is another object of the present invention to simplify construction of antenna assembly through use of known and traditional antenna, semiconductor, and electronic device fabrication techniques and technologies for production of multiple frequency band antennas.
Accordingly, another feature of the present invention is to provide a compact and effective family of designs for an antenna assembly operable in more than one frequency band.
Yet another feature and advantage of the present invention relates to a family or class of antenna assembly designs capable of conforming to existing structure of a compact WCD into which it is incorporated, including incorporating all components and electrical connections for the antenna assembly during original manufacture of the WCD on a common dielectric substrate member or members supporting the electrical circuit components of the WCD.
Still another feature of the present invention relates to the several effective antenna assembly embodiments thereof having no portion thereof external to the WCD and having no moving parts subject to breakage, wearing out, contamination from external sources, or other loss.
It is an additional object and feature of the present invention to provide an antenna assembly which may be incorporated into a compact, relatively thin WCD package and wherein the resonator element of the antenna assembly conforms to a sloping exterior dimension.
These and other objects, features and advantages will become apparent in light of the following detailed description of the preferred embodiments in connection with the drawings. Those skilled in the art of WCD antenna design will readily appreciate that these drawings and embodiments are merely illustrative and not intended to be limited as to the true spirit and scope of the invention disclosed, taught and enabled herein.